I was at the Grand Hyatt over Friday night. One caveat for travelers with rapidly upcoming stay plans: they're doing some construction on the lobby floor. (About a quarter of the lobby floor is blocked off with plastic sheets to reduce dust; I'm not sure what facility exactly is being renovated.) Other posts earlier in this thread have noted that you may want a non-Atrium room for noise reasons -- construction noise during business hours is yet another reason to avoid Atrium rooms, if you plan to spend much time in your room during those hours.
I noticed the thin inter-room walls as well; I checked in early and housekeeping was still working through the rooms on my floor (9th... a Gold Passport floor but not a club level since I'm still Platinum and not Diamond yet), and I could quite clearly hear the vacuum cleaner which was running in the room next door through the walls, not just the noise exiting the open door into hallway and coming back under my door. Fortunately I didn't have any noisy folks checked in next to me. I did notice the temperature control system had a feature I appreciated very much -- you can force the fan to run continuously at low or high settings instead of just the auto setting, and the resulting white noise is helpful for me when trying to get to sleep to ignore any television or other noise from adjacent rooms.